Vent filter members employing a water-repellent film are used in automotive electrical apparatuses and instruments, such as headlights, taillights, and fog lamps, motors, various pressure sensors, and pressure switches.
The filter members are also used in portable telephones, cameras, electric razors, and electric-powered toothbrushes.
These vent filter members are used for alleviating the variation of pressure in apparatuses which is caused by variation of temperature, for transmitting a voice or sound, or for releasing a gas generated inside, while preventing water and dust particles from coming into the apparatuses.
A prior art technique for attaching a water-repellent film to an apparatus is illustrated in FIG. 3. In this technique, a double-faced pressure-sensitive adhesive tape 1 is punched to form a hole of a given shape to thereby ensure the area of a vent hole 2. Thereafter, a water-repellent film 3 is bonded to the double-faced pressure-sensitive adhesive tape 1, and then punched to obtain a structure which is larger than the vent hole 2 and thereby has an application part. The resultant structure is fixed to an adhered through the application part of the double-faced pressure-sensitive adhesive tape 1 to simultaneously conduct sealing. This technique has been frequently used because of its inexpensiveness and the easiness of production.
However, there is a fear that the water-repellent film used in an automotive electrical apparatus or instrument or the like may suffer clogging as a result of wind and rain or of the adhesion of mud or an oil mist to thereby have reduced air permeability or reduced waterproofness. For avoiding the clogging, it has been necessary to prevent the water-repellent film from being directly exposed to a mist by fitting an L-shaped tube 5 to the mounting part of a base 4 as shown in FIG. 4 or by attaching a water-repellent film at the bottom of a labyrinth structure.
There also are mounting techniques for use in applications in which the pressure-sensitive adhesive may deteriorate by the action of heat or chemicals and finally peel off. In the case where a water-repellent film is to be attached to a base housing which is a thermoplastic resin molding, the film is fixed by thermal fusion. In the case where a water-repellent film is to be attached to a base 4 which is a metal such as an aluminum die cast, the water-repellent film 3 is fixed by caulking using a combination of a rubber packing 6 and a washer 7, as shown in FIG. 5.
As described above, in applications in which protection of a water-repellent film is necessary or a metallic base such as an aluminum die cast is used, there is a problem that additional parts and special jigs are necessary and highly precise temperature control is required. There is hence a desire for a vent filter member which can be easily mounted and fixed and is highly reliable.